A basement in a dream often represents what sits below ordinary awareness -- old fears, buried memories, or feelings you've stored away rather than dealt with. Discovering a room down there you didn't know existed can mirror the surprise of uncovering something in yourself you'd forgotten was still present.
Not only Trines and Sextiles may be counted friendly aspects, but even Squares and Oppositions too, if there happen a Reception. - Cardan Girolamo (1501-1576)